1. Field of the Invention
The present invention relates to a fuel injection control system and method for internal combustion engines, which compensates the fuel injection amount in response to changes in fuel injection timing dependent on operating condition of an internal combustion engine to improve vehicle drivability.
2. Description of Related Art
It is a general practice in a conventional fuel injection control for internal combustion engines to terminate fuel injection of a fuel injector at a fixed crankshaft angular position, so that all the required amount of fuel may be injected within the exhaust stroke of an engine which precedes the suction stroke. That is, the fuel injector is driven to start fuel injection before the intake valve opens. As a result, fuel injected from the fuel injector sticks or stays on the inside wall of an intake passage provided upstream of the intake valve, and then vaporizes and enters into the combustion chamber of the engine together with the intake air in the suction stroke of the engine.
It is a recent trend to control fuel injection timing variably in response to changes in the operating condition of the engine for improving vehicle drivability. In this system, the intake air flow speed, intake port temperature, intake valve temperature, fuel spray diffusion and the like changes in response to changes in fuel injection timing. Thus, the amount of fuel sticking or staying (fuel wetting) on the intake port changes responsively. This fuel wetting is likely to cause deviations of the actual air-fuel ratio of mixture supplied to the engine from a desired air-fuel ratio, particularly when the engine changes its operating condition.